Actually you can't take c4d's because they may have re-sized them or color balanced or something.

Basically don't take any layer.

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Uh, so what? If they did something to the resource, then whoever they got it from originally gave anyone permission to use it however, most likely. You can't just change the color of something to make it yours.

Uh, so what? If they did something to the resource, then whoever they got it from originally gave anyone permission to use it however, most likely. You can't just change the color of something to make it yours.

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Yes but it means you're going to be taking credit for doing work (changing color, layer masks, etc.) that isn't yours.
Also, there have been whole threads on this issue and it has been ruled that you can't take any layer from files that are for LRO.